A new attempt to refine gold

[WillGreen]

Dear All,

I am refining gold again, but this time I read Hokes.
I do have a question.
I started to work with 12 grams of 18K yellow gold, which I did not inquartate. I just cut the gold into fine pieces, put it in a flask, covered it with hydrochloric acid and added nitric acid until the reaction started. I added nitric acid several times, but always very little. The gold dissolved. I filtered the silver chloride out of the solution, added a couple of drops of sulphuric acid, brought the solution to a boil, let it cool and added a bit of hydrochloric acid. Now we come to the point where Hokes deals with driving off the excess of nitric acid. It is possible that there is an excess of nitric acid. If there is, it will be very little. Do I need to boil the solution down to a syrup? I do not completely understand what is happening during this step. Is there a possibility that I will evaporate some of the auric chloride, losing values? This may sound stupid, but I do not know the answer.
At this point the solution looks green and it is completely clear. What should I do next? Make a syrup or not? I do not have copperas. I can precipitate with SMB or with copper. Which one should I choose?

Thank you for reading. Best regards,

Will

 

[goldsilverpro]

Exactly how much nitric did it take? Assuming all the gold dissolved, if you didn't use over 11 or 12 ml of nitric, you probably won't need to evaporate.

 

[butcher]

Aww I spent all this time writing this before GSP posted, well I will post anyway.


You do not want to boil the solution, Notice in Hokes book she used a steam bath to evaporate the nitric acid from solution, the steam bath would not bring the solution to the boiling point to where you could lose values.

(In her book {Hoke's} the word boil in describing the process is the wrong term, she did not actually mean to boil she meant evaporate, on a steam bath)

We evaporate the solution below the boiling point of the solution.

If you sparingly added you’re nitric acid, you may not have as much nitric acid still in solution (as you would have had if you used 1 part nitric to 4 parts HCl).

A great way to deNOx the solution is to use the trick Harold taught us, add a gold button to use up the nitric acid, this method make removing the nitric acid fast and easy, this along with GSP’s advice of only using the nitric you need to put gold into solution.
These can save a lot of troubles.

When you first begin to evaporate the solution (not boil) you just want to see fumes evaporating, where the fumes will not carry metals or colored solutions, keeping the temperature below the boiling point, where if you actually boiled the solution the bubbles popping splashing, and carry over of metals in the fumes would occur, and with these boiling fume's carrying away some of your money.

When you first evaporate the solution it will boil off mostly water at first as the acid in solution concentrates, the water vapor fume's will contain some NOx gas and possibly HCl in these fumes, but mostly the acids HCl and nitric concentrate in solution will concentrate until most of the water is gone and the nitric begins to fume of as it breaks down as the solution is more concentrated, after the acids concentrate to the point they can no longer hold the acid at that concentration they begin to decompose the acid as concentrated acidic fumes, nitric will fume off after water, the nitric leaving solution as NOx gases (several of the nitrous oxide gases but mostly clear nitrous oxide NO and the red brown nitrous dioxide gas NO2), the solution getting fairly thick from evaporation the nitric will begin to try an leave the solution as a gas, (which all-most seems like, all at once, in one big boil-over), at this point there is a big chance of your solution boiling over and foaming most of your gold out of the pot, so being careful and keeping a close eye on the solution at this point can be important, an indication of the reaction is small bubbles begin to form just before solution boils over in a violent reaction, here I lower heat and have a spray bottle ready to calm the solution if needed, the water mist will break up the gas bubbles cool, and will dilute the solution if needed, after lowering temperature of the solution and letting the reaction go slowly evolving these NOx gases, after it is done, I can again raise back up the temperature as I am past the azeotropic point that this reaction occurs, this will remove the majority of the nitric but not all of it, The HCl additions will also release a red cloud on NO2, also the HCl addition adds some water in the acid, again diluting the remaining nitric in solution, which we will have to be concentrated again before NOx gases off, so we do not want to use a large excess of HCl here, evaporation (up to three cycles depending on how much nitric was added to dissolve the gold), (the last liquid to break down as gas in the evaporation is the HCl).

The few drops of sulfuric not only help to precipitate lead later, but can help to keep you from cooking your gold as dry salts as the sulfuric will not leave the solution easy, in fact sulfuric has a very high boiling point, this helps not only to keep the salts from forming so easy but also from drying out, if you made a mistake and concentrated your solution this far bringing them to the point of making a thick salt solution, instead of just the concentrated syrup solution.

With evaporation (not boiling) the metals will not leave the solution these metals salts stay in the concentrated liquid solution, but if you cooked this solution dry and then heated these gold chloride salts to the point of cooking them the chlorides could then gas off gold in the fumes as gold chlorides are volatile.

 

[TheGoldenChild]

Use UREA water solution to lower your PH to around 1 +/- .4 then drop with SMB I use something different but if you read you can find a better method. Another method is evaporating it until there is no more red gas coming off of it then the nitric is gone. DO NOT BOIL it is very dangerous also I recommend wearing a respirator rated for acid gases if you want to evaporate (3M makes a good respirator) if you don't plan on living very long don't worry about respirator.

 

[Geo]

Use UREA water solution to lower your PH to around 1 +/- .4 then drop with SMB I use something different but if you read you can find a better method. Another method is evaporating it until there is no more red gas coming off of it then the nitric is gone. DO NOT BOIL it is very dangerous also I recommend wearing a respirator rated for acid gases if you want to evaporate (3M makes a good respirator) if you don't plan on living very long don't worry about respirator.

good try. read Hole's book and try again.

no respirator will filter NO2 gas. let me repeat that, NO respirator will filter NO2 gas. its just giving you a false sense of security. if you smell nitric acid fumes, its too much. a person that is in good health should be able to detect about 2 PPM NO2 in the air. at 20 PPM, it can be fatal, so theres not a lot of room for error. please dont advise people to use a piece of safety equipment for a process that may kill them if it doesnt work.

 

[TheGoldenChild]

Use UREA water solution to lower your PH to around 1 +/- .4 then drop with SMB I use something different but if you read you can find a better method. Another method is evaporating it until there is no more red gas coming off of it then the nitric is gone. DO NOT BOIL it is very dangerous also I recommend wearing a respirator rated for acid gases if you want to evaporate (3M makes a good respirator) if you don't plan on living very long don't worry about respirator.

good try. read Hole's book and try again.

no respirator will filter NO2 gas. let me repeat that, NO respirator will filter NO2 gas. its just giving you a false sense of security. if you smell nitric acid fumes, its too much. a person that is in good health should be able to detect about 2 PPM NO2 in the air. at 20 PPM, it can be fatal, so theres not a lot of room for error. please dont advise people to use a piece of safety equipment for a process that may kill them if it doesnt work.

Given what he says buy a remote respirator. I use the 3M and smell no nitric but he is probally right. It supposed to remove hydrachloric acid fumes, I always used a strong fan when I removed nitric with heat.